Which terminals on an SPDT automotive relay serve as the Normally Open and Common terminals?

In the context of a Single Pole Double Throw (SPDT) automotive relay, the terminology “Normally Open” and “Common” refers to specific terminals that define the relay's operation.

The Common terminal is the point that connects to either the Normally Open (NO) or Normally Closed (NC) terminal, depending on the state of the relay. When the relay is not energized, the Common terminal connects to the NC terminal. However, once the relay is energized, it switches the connection from the NC terminal to the NO terminal.

In the case of the answer being B, it indicates that the terminals B and D are designated as the Normally Open and Common terminals, respectively. This configuration is typical in many automotive relay layouts, where one terminal (commonly referred to as the Common) serves as the switch point, and the other terminal is the Normally Open point, allowing current to flow only when the relay is activated.

Understanding this configuration is crucial for effectively utilizing relays in automotive applications, as it allows technicians to design circuits that control various functions, such as lights or motors, based on the relay’s operation. Recognizing how to identify these terminals on an SPDT relay helps ensure proper circuit function and can prevent wiring errors in installations.